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Dimetrodon had serrated teeth! Why is this news?

Figure 1. The serrated tooth of Dimetrodon — taken from a 2008 blog. Serrated teeth on Dimetrodon is old news, folks.

Try googling “Dimetrodon serrated” and you’ll get several pages of fresh-off-the-presses news about how exciting and important this new find is by Brink and Reisz (2014). Unfortunately, this is old news. Serrations on Dimetrodon teeth have been known for decades. The photo at left is from a 2008 blog.

What’s more exciting that finding serrations on a Dimetrodon tooth is witnessing the publicity machine whirling at Nature.com, the publisher of the article. It’s truly amazing.

Figure 2. Serrations on basal synapsids. Note serrations appear at the same time on the much smaller Secodontosaurus with ghost lineages for therapsids predating them both.

Brian Switek writing for National Geographic online summarized the paper noting that the big Dimetrodon was eating the big prey items including: “pinheaded protomammals called caseids” and “amphibians called diadectids.” We trashed the caseid/synapsid connection here. And the amphibian/diadectid connection here. Such old data from a respected news outlet takes us back to tail-dragging dino days.

From the abstract“Paleozoic sphenacodontid synapsids are the oldest known fully terrestrial apex predators. Dimetrodon and other sphenacodontids are the first terrestrial vertebrates to have strong heterodonty, massive skulls and well-developed labio-lingually compressed and recurved teeth with mesial and distal cutting edges (carinae). Here we reveal that the dentition of Dimetrodon and other sphenacodontids is diverse. Tooth morphology includes simple carinae with smooth cutting edges and elaborate enamel features, including the first occurrence of cusps and true denticles (ziphodonty) in the fossil record. A time-calibrated phylogenetic analysis indicates that changes in dental morphology occur in the absence of any significant changes in skull morphology, suggesting that the morphological change is associated with changes in feeding style and trophic interactions in these ecosystems. In addition, the available evidence indicates that ziphodonty evolved for the first time in the largest known species of the genus Dimetrodon and independently from the ziphodont teeth observed in some therapsids.”

What is intriguing is all the fuss about Dimetrodon grandis and D. limbatus having the oldest terrestrial serrations on the planet (that is, according to the headlines), when according to the Brink and Reisz charts, generic “therapsids” and Secodontosaurus had serrations earlier, at least according to their ghost lineages (Fig. 2).

What am I missing here?

Serrations are good for biting into big chunks of flesh, btw. Just ask any steak knife.

4 thoughts on “Dimetrodon had serrated teeth! Why is this news?”

The point was not that Dimetrodon has a knife edge on its teeth; as you say, that isn’t exactly the most thrilling news. The interesting bit is that Dimetrodon grandis had what is called ziphodonty. That is the serrations weren’t simply knife edges on the enamel as in Secodontosaurus and D.limbatus, but instead the denticles had their own dentine core and enamel cap. As they say in the discussion “There is an upper limit to the size of enamel prisms that can be deposited on teeth, and so to develop large structures such as denticles, the shape must be pre-formed by the dentine before enamel deposition.”
And although therapsids had a ghost lineage going back as far as sphenacodontids, their likelihood analysis (the pie charts on their phylogeny) suggests that serrations weren’t the primitive condition. Therefore D.grandis still represents the earliest appearance of “true” denticles.

Well, you asked what you were missing. Yes, there have been studies into the serrations, but this is the first that looks at the tooth histology and the first that demonstrates conclusively that what we see here is true ziphodonty rather than just a knife edge.

Whether you consider this newsworthy is up to you. I merely sought to correct your assumption (and, I admit, the assumption of most of the media) that the interesting bit was the presence of the serrations rather than the structure and development.